Hint for Section 7.3 Question 2

2. To show that a function f: XY is one-to-one, you usually suppose that x₁ and x₂ are elements of X such that f(x₁) = f(x₂) and show that x₁ = x₂.
To show that a function f: XY is not one-to-one, you usually find elements x₁ and x₂ in X so that f(x₁) = f(x₂) but x₁x₂.

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